Reflectix Single Bubble Foil Question

walhondingnashua

Feeling the Heat
Jul 23, 2016
331
ohio
As I am slowly finishing the inside of my garage (pole shed) I am working on the ceiling. The finished ceiling will be white interior grade steel with 1" of poly insulation that has 2 foil layers on each sheet. I will seal all the edges. Here is my question...

The builders used a layer of Reflectix single bubble wrap directly under the roof layer as a vapor barrier. There was a lot left over and I stapled what was left to the bottom of the trusses and it will between my ceiling steel and the insulation sheets. There was enough to do 3/5th of the ceiling. There are mixed opinions online about the benefits of this stuff. Is it worth it for me to buy more to finish the ceiling or am I just wasting money with the way I am insulating?
 

festerw

Feeling the Heat
Nov 16, 2009
467
Cambridge Springs, PA
I didn't use the bubble foil but I used a radiant barrier sheet on the underside of my joists after retrofitting radiant heat.

It made a significant difference in the amount of heat coming into the basement and raised the floor temp 5 degrees.

I could see it helping with temps in the summer with proper roof venitlation.
 

semipro

Minister of Fire
Jan 12, 2009
3,938
SW Virginia
There are mixed opinions online about the benefits of this stuff. Is it worth it for me to buy more to finish the ceiling or am I just wasting money with the way I am insulating?
While Reflectix might make a useful radiant barrier (only with a corresponding adjacent air gap) or vapor barrier, it doesn't provide much thermal insulation, not as much as they advertise anyway.
Your money is probably better spent on a dedicated radiant/vapor barrier.
The expert opinions on Reflextix aren't really that mixed. It's way overrated and overused.
 
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snaple4

Feeling the Heat
Dec 18, 2017
279
AR
the stuff works great compared to nothing. Correct me if I have this wrong; You have your ceiling Sheetrock, then ceiling joists, then layer of bubble, then space up to roof rafters, then bubble o top of roof rafters, then roof?

If no other insulation then the bubble stuff on top ceiling rafters will make all the air between the Sheetrock and bubble a layer of insulation (assuming it is properly sealed) that equals roughly R1/inch...
 

ozarkoak

New Member
Nov 1, 2020
21
Arkansas
the stuff works great compared to nothing. Correct me if I have this wrong; You have your ceiling Sheetrock, then ceiling joists, then layer of bubble, then space up to roof rafters, then bubble o top of roof rafters, then roof?

If no other insulation then the bubble stuff on top ceiling rafters will make all the air between the Sheetrock and bubble a layer of insulation (assuming it is properly sealed) that equals roughly R1/inch...
I used it in more of a radiant way. I lined my well house ceiling and walls. Usually a heat lamp was needed to prevent the well from freezing. Now the pressure tank which admittedly is large, provides enough warmth that the heater has not turned on this year.
 

semipro

Minister of Fire
Jan 12, 2009
3,938
SW Virginia
the stuff works great compared to nothing.
Agreed, but you'd get 6 times the R-value from foil-covered polyiso foam board for the same money.

...If no other insulation then the bubble stuff on top ceiling rafters will make all the air between the Sheetrock and bubble a layer of insulation (assuming it is properly sealed) that equals roughly R1/inch...
An air space larger than about 1 in. loses effectiveness beyond R1 because of convective heat transfer within the space. If what you are saying was true no one would fill the space between their studs with insulation. They'd just seal up the sheathing and drywall.
 

peakbagger

Minister of Fire
Jul 11, 2008
5,795
Northern NH
Years ago I saw a demo that some college student did where he insulated a wall with sheets of plastic. He just filled the cavity with plastic sheets separated by 3/4" spacers. It was quite effective. He then went to 1" spacers and lost performance. I think he also did 1/2" spacers which had less of an impact.
 

SpaceBus

Minister of Fire
Nov 18, 2018
5,165
Downeast Maine
Years ago I saw a demo that some college student did where he insulated a wall with sheets of plastic. He just filled the cavity with plastic sheets separated by 3/4" spacers. It was quite effective. He then went to 1" spacers and lost performance. I think he also did 1/2" spacers which had less of an impact.
Sounds like a decent system for an animal house or maybe a heated shop.
 

walhondingnashua

Feeling the Heat
Jul 23, 2016
331
ohio
The finished ceiling will be ribbed steel just like the exterior roofing and siding, but with white paint and no warranty. The main layer of insulation will come from 1" foil covered polyiso like the garage walls. I only put the bubble foil up because it was left over and didn't know if it was worth having more than 1 radiant barrier.
 

Grizzerbear

Minister of Fire
Feb 12, 2019
817
SW Missoura
I have it under the metal siding and roof panels of my house. Shiny tin foil side facing towards the outside. It makes a hell of a difference on reflecting......not sure that's the word I'm looking for......heat away from the building. That said I dont think an extra layer for radiant purposes would increase the effectiveness much. It won't do much as far as insulating either but then again it certainly won't hurt.